Galactose Fermentation Test

The purpose is to see if the microbe can ferment the carbohydrate (sugar)galactoseas a carbon source.

How isgalactosefermentation determined?

Ifgalactoseis fermented to produce acid end products, the pHof the medium will drop. A pHindicator in the medium changes color to indicate acid production.

What medium is used?

Several media are available for this. Most commonly used isphenol red galactose broth.The medium is a nutrient broth to which 0.5-1.0%galactoseis added. The pHindicator phenol red is red at neutral pHbut turns yellow at pH<6.8. It also changes to magenta or hot pink at pH>8.4.

How is the test performed?

An inoculum from a pure culture is transferred aseptically to a sterile tube ofphenol red galactose broth.The inoculated tube is incubated at 35-37C for 24 hours and the results are determined. A positive test consists of a color change from red to yellow, indicating a pHchange to acidic.

What reagents are added?

None.

To perform this test in VirtualUnknown™ Microbiology, complete the following steps: